Fibroblast Growth Factor Receptor 2 (FGFR2), also known as BEK, BFR-1, CD332, CEK3, CFD1, ECT1, FLJ98662, JWS, KGFR (also known as FGFR2(IIIb)), K-SAM, TK14, and TK25, is one of four highly conserved receptor tyrosine kinases (FGFR1, FGFR2, FGFR3 and FGFR4) that mediate fibroblast growth factor (FGF) signaling by binding FGFs. The FGF receptors are characterized by two or three extracellular immunoglobulin-like domains (IgD1, IgD2 and IgD3), a single-pass transmembrane domain, and a cytoplasmic tyrosine kinase domain. FGF ligand binding induces FGF receptor dimerization and tyrosine autophosphorylation, resulting in cell proliferation, differentiation and migration (Turner et al. (2010) NATURE REVIEWS CANCER 10:116-129; Beenken et al. (2009) NATURE REVIEWS DRUG DISCOVERY 8:235-254; Gomez-Roman et al. (2005) CLIN. CANCER RES. 11:459-65; Chang et al. (2005) BLOOD 106:353-6; Eswarakumar et al. (2005) CYTOKINE GROWTH FACTOR REV. 16:139-49).
Alternative splicing in the IgD3 domain yields either the IIIb or IIIc isoform of FGFR1, FGFR2 and FGFR3. The FGFR4 gene is expressed only as the IIIc isoform. The different isoforms of FGF receptors exhibit tissue-specific expression, and they respond to a different spectrum of 18 mammalian FGFs (Beenken et al., supra). Binding of FGFs to FGFRs in the presence of heparan sulfate proteoglycans induces autophosphorylation of FGFRs at specific intracellular tyrosine residues. This causes phosphorylation of adaptor molecules, such as FGFR substrate 2α (FRS2α), which recruits other proteins to activate various signaling cascades, including the mitogen-activated protein kinase (MAPK) pathway and the phosphoinositide 3-kinase (PI3K)/Akt pathway (Beenken et al., supra; Eswarakumar et al., supra; Turner et al., supra).
It has been suggested that the dysregulated FGF signaling can directly drive the proliferation of cancer cells, promote the survival of cancer stem cells, and support tumor angiogenesis (Turner et al., supra). FGFR2 signaling appears to play a role in cancer. Missense mutations in the FGFR2 gene occur in various cancers, including endometrial cancer (Pollock et al., 2007, ONCOGENE 26:7158-7162; Dutt et al., 2008, PROC. NATL. ACAD. SCI. USA 105:8713-8717), ovarian cancer, breast cancer, lung cancer (Greenman et al., 2007, Nature 446:153-158; Ding et al., 2008, NATURE 455:1069-1075; Davies et al., 2005, CANCER RES. 65:7591-7595) and gastric cancer (Jang et al., 2001, CANCER RES. 61:3541-3543). Some of these activating mutations also have been reported in patients with skeletal disorders (Dutt et al., supra). Two independent genome-wide association studies have linked specific single nucleotide polymorphisms (SNPs) in the FGFR2 gene to increased susceptibility to breast cancer (Easton et al., 2007, NATURE 447:1087-1093; Hunter et al., 2007, NAT. GENET. 39:870-874). These cancer-associated SNPs appear to elevate FGFR2 gene expression (Meyer et al., 2008, PLOS BIOL. 6:e108). The FGFR2 gene, located at human chromosome 10q26, is amplified in a subset of breast cancers (Adnane et al., 1991, ONCOGENE 6:659-663; Turner et al., 2010, ONCOGENE 29:2013-2023) and gastric cancer (Hara et al., 1998, LAB. INVEST. 78:1143-1153; Mor et al., 1993, CANCER GENET. CYTOGENET. 65:111-114).
Naturally occurring antibodies are multimeric proteins that contain four polypeptide chains (FIG. 1). Two of the polypeptide chains are called immunoglobulin heavy chains (H chains), and two of the polypeptide chains are called immunoglobulin light chains (L chains). The immunoglobulin heavy and light chains are connected by an interchain disulfide bond. The immunoglobulin heavy chains are connected by interchain disulfide bonds. A light chain consists of one variable region (VL in FIG. 1) and one constant region (CL in FIG. 1). The heavy chain consists of one variable region (VH in FIG. 1) and at least three constant regions (CH1, CH2 and CH3 in FIG. 1). The variable regions determine the specificity of the antibody. Naturally occurring antibodies have been used as starting material for engineered antibodies, such as chimeric antibodies and humanized antibodies.
Each variable region contains three hypervariable regions known as complementarity determining regions (CDRs) flanked by four relatively conserved regions known as framework regions (FRs). The three CDRs, referred to as CDR1, CDR2, and CDR3, contribute to the antibody binding specificity.
Inhibitory antibodies specific against human FGFR2 have been difficult to generate because of the high homology between mouse and human FGFR2. In particular, the ligand binding domain of the mouse and human FGFR2 shares approximately 98% sequence identity (Wei et al., 2006, HYBRIDOMA 25:115-124). Thus, there is a need for improved FGFR2 antibodies that can be used as therapeutic agents.